BBC Radio 1 has drafted in a new generation of presenters including Fearne Cotton and Greg James, but is still failing to reach its target audience, a BBC trustee has warned.

David Liddiment said the average age of the Radio 1 listener was 30 – against a target age group of 15 to 29 – the same as it was when he conducted a review of the station two years ago.

"It hasn't got any worse but it hasn't got any better," Liddiment told the Voice of the Listener and Viewer spring conference in central London on Tuesday. "The average age remains 30 and it still remains a challenge. We are in dialogue with management how to achieve this."

Asked if 37-year-old breakfast DJ Chris Moyles, recently reported to have signed a new two-year deal with the station, was hindering a shift to a younger audience, Liddiment said: "It did freshen up its presenting team immediately after the trust review – a number of people left the station and a number of new people came.

"It's not for the BBC Trust to tell the station who it should hire and who it shouldn't hire. What there is is an acknowledgement that the average age is still about 30 and we are interested in hearing what steps the BBC management will take to keep the focus on a younger age. That is what the station is there to do."

Liddiment said changing the demographic appeal of a station "isn't always just a question of playing this rather than that or a tweak here and a tweak there".

"Sometimes [it requires] a proper understanding of changes in behaviour and it may well be that something of that kind would apply here," he added. "It's not so much the age [of the DJ] as their style and ability to connect with the audience."

Liddiment reiterated concerns that BBC Radio 4 should also extend its appeal to a younger audience after the proportion of its listeners aged between 35 and 54 fell from 33% in 2000 to 26% last year.

He said it was essential for the future health of the station that it appealed to its listeners of the future. "This age group feeds Radio 4's core audience and it would in my judgment be negligent not to [look at this]," Liddiment added.

He said changes to the station included making it less studio- and London-based, with a "continued drive to make the network's tone more welcoming, spontaneous and at times a little less formal".

"Radio 4 is a national treasure but it is not one set in aspic," said Liddiment, adding that he was not asking for radical changes to the station's output.

"No one is suggesting the whole station changes its tone of voice," he said. "What is being suggested by management is that in some places where it is appropriate they will try to make the tone a little less formal."

Liddiment added that more than half the station's current audience was over 55 and said it would continue to serve that demographic in the future.

He used the example of Home Truths, the acclaimed Radio 4 Saturday morning show fronted by the late John Peel, as an example of a way in which the station could subtly change its tone without altering the overall feel of the station.

He added: "You will not wake up tomorrow to find Chris Moyles presenting the Today programme, nor do we want to reduce Radio 4's intelligence, analysis and ambition."

A BBC spokeswoman said: "As the trust recommended, Radio 1 has successfully renewed its focus on the younger end of its target audience over the past two years and now reaches almost half the country's 15- to 24-year-olds and a third of all 10- to 14-year-olds. While it's a well understood social phenomenon that people increasingly want to stay connected to young brands like Radio 1 as they grow older, we are working hard to attract young listeners through exciting, distinctive programmes, new talent and unrivalled events."

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